SUBUNIT COMPOSITION OF THE CRUSTACEAN HEMOCYANINS - DIVERGENCE IN INCIPIENT SPECIATION

The monomeric subunit composition of the oxygen carrier hemocyanin was examined in samples of the Sesarma reticulatum complex and of Uca min ax, both of which are believed to be in the process of speciation. The samples were taken on the Atlantic and Gulf of Mexico coasts, from di sjunct populations that are believed to have been isolated by the Flor ida peninsula since the retreat of the last glacier. In Atlantic and G ulf samples of the S. reticulatum complex, which is believed to be in the terminal stages of speciation, the hemocyanins differed qualitativ ely. Several electrophoretic bands found in one group, including an in variant band, were totally absent from the other. This difference exce eds that reported in a previous investigation of a variety of polymorp hic allozymes in this species complex. It also exceeds the physiologic ally labile differences in hemocyanins found previously within a panmi ctic species of brachyuran crustaceans. In U. minax, which is believed to have diverged less, Atlantic and Gulf animals expressed the same n umber of electrophoretic bands at exactly the same positions. Nonethel ess, highly significant differences in band frequencies distinguished both Atlantic samples from the Gulf sample, and somewhat less signific ant differences distinguished the Atlantic cold temperate zone samples from the warm temperate zone ones. The phenotypes of the major bands, defined as those present in high densities, qualitatively distinguish ed Atlantic from Gulf animals, but they did not differentiate the two Atlantic samples. The difference between Atlantic and Gulf members of this species also exceeds that found previously among polymorphic allo zymes. These findings further support the hypothesis that the hemocyan ins are among the first proteins to diverge structurally in brachyuran speciation.